Hybrid automotive powertrains generally provide higher fuel mileage and lower emissions compared to fully internal combustion (IC) powertrains. Hybrid powertrains generally combine two or more energy sources/systems such as a battery powered electric motor and a highly efficient IC engine. On-board computer controls can be used to control when the two systems are used so as to achieve peak driving efficiency in different driving conditions.
To maximize fuel economy, it is desirable that the hybrid powertrain have the ability to rapidly stop and start the IC engine. For example, the IC engine is turned off during deceleration and restarted when the driver releases the brake or presses on the accelerator. Electrical power accumulated by the deceleration is used to restart the IC engine. However, because of the short time between stops and starts, and the degree of electrical power necessary to restart the IC engine, the IC engine is generally in an instant-off state where at least the intake manifold of the IC engine will not be clear of recirculated exhaust (exhaust gas recirculation—“EGR”) or purge materials such as fuel vapor or gases. On restart, the presence of those EGR and purge material in the intake manifold can decrease overall fuel economy and increase undesirable emissions.